It's closer to the quality of a display then just how small your pixels are. It determines how large your display is before you get too many dead-pixels (yield in fabrication). What range of colors your pixels can produce (electric properties? resistance, leakage, etc.). Whether you can blast all pixels at full brightness, or only a few (thermal properties). And indeed, resolution of the display (size of transistors).

What is missing from this analogy is the degree of layering / 3d structures that is possible. You might couple that to RGB v RGBY but I'm not really sure.